To the Editor.—Since the introduction in 1968 of the bronchofiberoscope, the procedure has been readily accepted and much used. However, little has been said about the potential hazards.The clinical applications have been well outlined by Dr. Renz and associates (219:619, 1972), Dr. Tahir (220:725, 1972), and by Drs. Matsumoto and DeLaurentis (221:1163, 1972).Matsumoto and DeLaurentis's and our own observations of continuously monitored patients during bronchofiberoscopy suctioning has revealed transient falls in arterial oxygen tension of over 20% of control values. Renz has pointed out the necessity of maintaining the minute ventilation in the mechanically supported patient. Here, a note of caution needs to be emphasized regarding the nonsupported patient's ability to maintain his own minute ventilation.The magnitude of minute ventilation removed via bronchoscope with 2-mm suction port at various vacuums is dramatically represented in the Figure.A commonly available suction machine has the capability of producing